Recent innovations in less invasive methods of performing surgery have led to significantly reduced costs and complications, thus motivating further research in minimally invasive methods to replace some conventional surgeries. We have demonstrated a novel solution for online monitoring and control of thermal surgery using focused ultrasound beams. This method offers completely noninvasive, controllable and accurate coagulation of tissues even deep within the body. During the test procedures in animals, we have used online magnetic resonance imaging (MRI) to monitor temperature elevation during sonication and to delineate tissue necrosis. In view of the success of these tests, this application proposes a twofold development of the procedure. First, we propose further animal studies to establish the safety of the procedure and to correlate the MRI information with the histologic effects of the sonication. These studies will investigate both the acute and long-term effects of the sonications. The experiments will be performed in different organs and will correlate with the project 1 studies using other invasive thermal techniques (laser) for tissue destruction. In addition, the effects on critical structures, such as bone and blood vessels, will be investigated. Second, parallel to the animal experiments, we propose a clinical feasibility study to answer many clinical questions (What happens to the necrosed tissues? How painful is the treatment? Is general anesthesia required or is sedation adequate?). We plan to treat small fibroadenomas of breast during this phase I/II study. Running the clinical and animal studies in parallel will allow us to obtain answers quickly so that the tumors which would benefit most from the therapy can be treated immediately when this study is completed. The anticipated advantages of this study using MR guided focused ultrasound are: First, high spatial accuracy will be possible due to high soft tissue contrast of MRI. Second, the temperature sensitivity of MRI can be used to monitor the temperature elevation in surrounding normal tissues to increase safety. Third, lower power test pulses can be used to verify the focal location prior to the high power exposure. Fourth, the recovery time, hospital stay, and risk for infection and other complications will be reduced when compared with conventional surgery. Finally, successful implementation of such a noninvasive procedure will significantly reduce the cost of medical care for these patients.